This invention relates generally to implantable medical electrical leads, and more particularly to implantable leads employing screw-in fixation mechanisms and to multi-conductor leads.
In implantable leads employing helical fixation members, twisting of the lead body due to applied torque makes implanting the lead more difficult for the physician. This is true whether the fixation mechanism is coupled mechanically to the lead body and rotated by rotation of the lead body itself, as in U.S. Pat. No. 5,076,285, issued to Hess et al. or the fixation mechanism rotated by means of a rotatable conductor located within the lead body as in U.S. Pat. No. 4,106,512, issued to Bisping. In the former case, twisting of the lead body due to torque applied at the proximal end results in the number of turns or rotations of the proximal end of the lead not corresponding to the number of turns of the distal end of the lead body carrying the helix. In the latter case, twisting of the lead body due to torque applied by the rotatable conductor along the length of the lead results in the number of turns or rotations of the proximal end of the rotatable conductor not corresponding to the number of turns or rotations of the helix relative to the distal end of the lead. In the context of leads employing rotatable fixation helixes, one approach to dealing with the problems due to the interaction of the rotatable conductor and the lead body has been to provide a slippery surface either on the conductor itself as in U.S. Pat. No. 5,456,707 issued to Giele or on the interior of the lead body as disclosed in U.S. Pat. No. 5,476,501 issued to Stewart et al.
In implantable leads employing multiple conductors, a wide array of configurations have been proposed, including co-axially arranged coils as in U.S. Pat. No. 4,355,646, issued to Kallok, conductors located in parallel lumens within the lead body, as in U.S. Pat. No. 4,135,518, issued to Dutcher and conductors embedded in the wall of the lead body, as in U.S. Pat. No. 4,840,186, issued to Lekholm et al. A two-piece lead body in which conductors are located between a ridged inner tubular member and an outer tubular member has been employed in implantable neurological leads and is disclosed in FIGS. 7 and 8 of Pending Provisional Application Serial No. 60/033,511, filed on Dec. 19, 1996 by Cross et al.